A digital copying machine known as one of the image processing apparatuses is furnished with a scaling function that allows an output of an enlarged or reduced image of the original. A digital copying machine of this type includes, as shown in FIG. 48, an original image memory 101 for storing image data inputted into the digital copying machine, a scaling processing section 102 for carrying out scaling processing, and a scaled image memory 103 for storing scaled image data. To be more specific, when an enlarged copy is made by this digital copying machine, the image data are retrieved from the original image memory 101, enlarged by the scaling processing section 102, and stored in the scaled image memory 103.
However, according to this arrangement, the digital copying machine must have the original memory 101 and scaled image memory 103 separately, thereby increasing the number of memories and hence the cost of the resulting digital copying machine.
To eliminate this problem, Japanese Examined Patent Publication No. 3-74549 (1991) proposes an arrangement, wherein a single memory is provided for storing both the original image data and the scaled image data obtained as a result of the enlarged-scaling processing. According to this arrangement, the image data are enlarged in the manner illustrated in FIG. 49. That is to say, when the image data stored in lines Y.sub.1 -Y.sub.n on the image memory 111 are enlarged, the enlarged-scaling processing starts with the line Y.sub.1, the line containing the image data located in the remotest place from the reference point S, so that the scaled image data are steadily produced and written into lines Y.sub.1 '-Y.sub.n ' sequentially in ascending order over the memory region where the original image data were stored.
This arrangement can reduce the number of memories. However, it becomes necessary to match a capacity of the image memory 111 with an increase of the image data volume as a result of the enlarged-scaling processing, in other words, the image memory 111 must increase a capacity in proportion to magnification. This undesirably increases the cost of the image memory 111, and hence makes the resulting digital copying machine more expensive.